This invention relates to a color image pick-up apparatus for obtaining color television signals using a separate luminance system.
In a prior art color image pick-up apparatus incorporated in a separate luminance system, an optical filter generally called a luminance filter (Y filter) was used in a luminance signal path to act as the color filter. Generally placed in the color signal path was a repetition of a red filter and a blue filter, or a repetition of a red filter, green filter, and blue filter. These systems are called a Y-RB system or a Y-RGB system. In the use of the color image pick-up apparatus of the type described above for the purpose of obtaining a luminance signal Y, the picked up signals are passed through a Y filter having a visual sensitivity characteristic resulting in light loss which occurs on the short wavelength side as well as on the long wavelength side. Moreover, as the picked up signals are passed through a red light transmitting filter, a green light transmitting filter, and a blue light transmitting filter for the purpose of obtaining R, G and B color signals, light components other than transmitted light are lost. Accordingly, the light utilization factor of the color image pick-up apparatus is low which is extremely disadvantageous from the standpoint of sensitivity. In order to improve the sensitivity, a method has been proposed wherein a cyan light filter and a yellow light filter are used as color filters in the color signal path. Usually, in this method, a red signal or a blue signal is modulated with a carrier wave frequency determined by the pitch of a repetitive filter arrangement which passes all visible light. Accordingly, the red signal and the blue signal exist in a higher frequency region of the image pick-up apparatus output signal. When demodulating respective color signals back to the image frequency band, noise in that higher frequency band is then converted into a lower frequency band. This, in turn, causes a degrading of the color signals signal-to-noise ratio. Also, it can be readily understood that as the frequency of the output of the image pick-up device (including a preamplifier) increases, the noise level also increases.